Polyacetal resins have various excellent properties and molded articles thereof are utilized in wide-ranging fields, but in association with the dramatic development of technology in the field of application, there is a tendency to demand more excellent properties for polyacetal resin materials to be used. In the field of application for automobile interior decorative parts and the like, there has been such a demand for polyacetal resin materials which have excellent heat stability, the reduced generation amount of volatile organic compound from that resin, an excellent weathering resistance and further a metallic appearance for imparting a luxurious taste.
To cope with those matters above, a variety of improving methods have been known to each individual property demanded.
For example, to improve heat stability polyacetal resin, hindered phenol-based compounds as an antioxidant, nitrogen-containing compounds such as melamine and polyamides as a heat-resistant stabilizer, and other compounds such as oxides, hydroxides, inorganic acid salts and carboxylates of alkaline-earth metals have generally been blended.
Further, to reduce the generation amount of formaldehyde as a volatile organic compound, there are disclosed polyacetal resin compositions containing varieties of compounds. For example, there are disclosed: a polyacetal resin composition containing a polyacetal resin and a glyoxy-diureido compound (JP-A 10-182928 (Claim 1)); a polyacetal resin composition containing a polyacetal resin, and a cyclic nitrogen-containing compound (glycocyamidine such as creatinine, or a derivative thereof) (JP-A 11-335518 (Claim 1)); a polyacetal resin composition containing a polyacetal resin, at least one processing stabilizer selected from polyalkylene glycol, fatty acid ester, fatty acid amide, and fatty acid metal salt, and at least one suppressor selected from urea, a derivative thereof, and an amidine derivative (JP-A12-26704 (Claim 1)); a polyacetal resin composition containing a polyacetal resin, a hindered phenol-based compound, a spiro compound having triazine ring, and at least one of processing stabilizer and a heat-resistant stabilizer (JP-A 2003-113289 (Claim 1)); and a polyacetal resin composition containing a polyacetal resin, and a guanamine derivative such as benzoguanamine a stabilizer (JP-A 62-190248 A). In addition, JP-A 2005-112995 discloses a polyacetal resin composition composed of a polyacetal copolymer having a specific terminal group, and a formaldehyde inhibitor, with the disclosure of a guanamine compound, a urea-based compound, and a carboxylic acid hydrazide-based compound as the formaldehyde inhibitor.
In addition, in order to improve the weathering resistance of polyacetal resin, JP-A 61-36339 discloses a composition obtained by adding a benzotriazole-based material or the like and a hindered amine-based material to polyacetal resin to coexist. Further, JP-A 6-256623 discloses a composition for which weathering (light) resistance and thermal stability have been improved by blending an antioxidant, tetrakis[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)-propionate]methane, a light stabilizer, bis-[N-methyl-2,2,6,6-tetramethyl-4-piperidinyl sebacate, and a UV absorber, 2-[2′-hydroxy-3′,5′-bis-(α,α-dimethylbenzyl)phenyl]benzotriazole.
According to the techniques disclosed in these documents, it is possible to significantly reduce the generation of formaldehyde from polyacetal resin, and furthermore, it is possible to impart excellent weathering resistance to polyacetal resin.
Only a simple combination of these techniques can not bring, however, the additive property of effects into existence. In particular, when a hindered phenol and a hindered amine are used in combination, an opposing effect lowers thermal stability and light stability, thereby making it very difficult to obtain a resin substance having excellent weathering resistance, significantly suppressing the generation of formaldehyde, and having no such problem as defective appearance due to the bleeding of blending components.
Further, as a method for imparting a metallic appearance to polyacetal resin, only applying coating or metal plating onto a molded article is known and polyacetal resin material for imparting a metallic appearance without the need of these secondary processing has not been known.